Thought this was a damn fun subject. Unfortunately there's quite a few fights missing on the original article so I took the initiative to add in my own in bold.

Most mixed martial arts matchups are emotionally charged enough, as two finely tuned professional athletes enter a foreboding cage or ring to throw fists, feet, knees and elbows at one another after months of mental preparation and long hours at the gym. When the recipe includes vengeance, the situation becomes downright explosive.

10. Fedor Emelianenko vs. Tsuyoshi Kosaka
Pride “Bushido 6” | April 3, 2005 -- Yokohama, Japan
For nearly a decade, it was the sore thumb on Emelianenko’s otherwise-pristine resume. Kosaka’s elbow -- which most concede was an illegal blow -- sliced through the flesh above the Russian’s right eye 17 seconds into their encounter at a Rings event in 2000, resulting in Emelianenko’s first defeat. A little more than four years later, “The Last Emperor” exacted terrible justice inside Pride Fighting Championships, as he brutalized the Japanese veteran for 10 minutes en route to a doctor’s stoppage.

9. Tito Ortiz vs. Guy Mezger
UFC 19 “Ultimate Young Guns” | March 5, 1999 -- Bay St. Louis, Miss.
A late replacement for the injured Vitor Belfort, Ortiz stopped Mezger on punches 9:56 into the first round of their rematch. Afterward, “The Huntington Beach Bad Boy” unfurled both middle fingers in the direction of Mezger’s corner, fanning the flames of his infamous rivalry with the Lion’s Den and its frontman, Ken Shamrock. The victory avenged Ortiz’s first career setback, a guillotine choke-induced submission to Mezger at UFC 13. He went on to beat Shamrock three times.

Velasquez's revenge was brutal.
8. Cain Velasquez vs. Junior dos Santos
UFC 155 “Dos Santos vs. Velasquez 2” | Dec. 29, 2012 -- Las Vegas
Velasquez lasted just 64 seconds against dos Santos at UFC on Fox 1 in November 2011. After handing Antonio Silva a horrific beating six months later, the American Kickboxing Academy ace was in position for a rematch, and he made the most of his opportunity. Velasquez battered dos Santos for five rounds and secured a surprisingly one-sided unanimous verdict at UFC 155, as he captured the Ultimate Fighting Championship’s heavyweight crown for a second time.

7. Georges St. Pierre vs. Matt Serra
UFC 83 “Serra vs. St. Pierre 2” | April 19, 2008 -- Montreal
Generations from now, it may still rank as the most shocking upset in MMA history. On April 7, 2007, Serra climbed into the cage in Houston as an 11-to-1 underdog and left as the welterweight champion, having stunned St. Pierre with a first-round technical knockout in the UFC 79 main event.

The fairy tale was short-lived, however, as the French Canadian reclaimed his belt a year later, stopping Serra on a series of vicious knees to the body at UFC 83. St. Pierre has held the 170-pound belt ever since.

6. Chuck Liddell vs. Tito Ortiz
UFC 47 “It’s On” | April 2, 2004 -- Las Vegas
The long-awaited Liddell-Ortiz showdown finally materialized at the Mandalay Bay Events Center in Sin City. Pre-fight posturing built anticipation to a fever pitch. Ortiz claimed he and Liddell, as friends and former training partners, had made a pact never to fight one another. Liddell denied those claims and accused Ortiz of ducking the fight. “The Iceman” finished it 38 seconds into round two with a wicked volley of punches that still makes the rounds on the UFC highlight reels.

5. Brock Lesnar vs. Frank Mir
UFC 100 “Lesnar vs. Mir 2” | July 11, 2009 -- Las Vegas
A former World Wrestling Entertainment superstar, Lesnar made his ballyhooed Octagon debut with just one professional fight under his belt in February 2008. Mir welcomed him rudely, as he submitted the hulking South Dakota native with a kneebar 90 seconds into round one. After decisive wins over Heath Herring and Randy Couture, a wiser and more measured Lesnar took a second swipe at Mir at UFC 100 a year and a half later, mauling the Brazilian jiu-jitsu black belt with thudding ground-and-pound on his way to a second-round stoppage.

St. Pierre delivered in the rematch.
4. Georges St. Pierre vs. Matt Hughes
UFC 65 “Bad Intentions” | Nov. 18, 2006 -- Sacramento, Calif.
St. Pierre, who submitted to a Hughes armbar at UFC 50, had to wait more than two years for the chance to avenge his first career defeat. Hughes stoked the French Canadian’s competitive fires in the weeks leading into the rematch, questioning St. Pierre’s heart and desire. At UFC 65, “Rush” answered those criticisms in resounding fashion, as he wiped out Hughes with an exquisitely executed head kick and follow-up punches and elbows on the ground.

3. Anderson Silva vs. Chael Sonnen
UFC 148 “Silva vs. Sonnen 2” | July 7, 2012 -- Las Vegas
No one has come closer to beating Silva inside the UFC than Sonnen, who was less than half a round away from springing the upset at 117. Alas, “The Spider” pulled the proverbial rabbit -- a fifth-round triangle choke -- out of his hat and snatched victory from the jaws of defeat.

Victories against Brian Stann and Michael Bisping put Sonnen in position to pine for the rematch, and Zuffa brass obliged in the summer of 2012. Their second meeting was far less dramatic, as Silva dispatched the mouthy Oregonian with a knee to the body and subsequent punches in round two.

2. Quinton Jackson vs. Wanderlei Silva
UFC 92 “The Ultimate 2008” | Dec. 27, 2008 -- Las Vegas
In two previous matchups under the Pride Fighting Championships banner, Silva had wiped the mat with “Rampage.” His brutal finish on Jackson at Pride 28 “High Octane” in 2004 remains one of the most violent and memorable knockouts in MMA history. Act three of their trilogy unfolded within the confines of the Octagon and took a far different turn. A little less than three and a half minutes into their UFC 92 encounter, Jackson connected cleanly with a rolling left hook that rendered “The Axe Murderer” unconscious and provided “Rampage” with a taste of sweet revenge.

1. Chuck Liddell vs. Randy Couture
UFC 52 “Couture vs. Liddell 2” | April 16, 2005 -- Las Vegas
Couture had never been cleanly knocked out, until he ran into Liddell’s lethal right hand at the MGM Grand Arena. “The Natural” had embarrassed Liddell two years earlier, as he buried him with third-round punches and captured the interim light heavyweight crown in the process. The rematch, however, belonged to Liddell. After an accidental eye poke resulted in a brief respite, “The Iceman” clipped the oncoming Couture with a left hook and then waylaid him with a right cross. Arriving on the heels of “The Ultimate Fighter” Season 1 and carried by a main event heavy on star power, UFC 52 was the first Ultimate Fighting Championship event in history to draw more than 300,000 pay-per-view buys and helped launch the promotion to new heights.

Honourable mention:
Vitor vs Randy Couture
Big Nog vs Frank Mir (He had Frank hurt badly. If the ref didn't say anything he would have won the fight. The ref said "not the neck/back of the head" which is koo, but that made Big Nog freeze and in the split second he opted for the guillotine which led to the infamous reversal. Talk about irony.)

Out of all of these rematches I would have to say GSP vs Serra was the most satisfying followed by Anderson vs Okami cuz that was six long years he had to wait to avenge that DQ loss. As for the most entertaining it had to be Brock vs Mir. That was real bad blood between the two that probably still lingers.

I know that revenge wasn't an accurate description of the following fight but Hughes versus Trigg 2 was a good one. Trigg kicks Hughes in the nuts, almost submits him in a rear naked, then Hughes picks him up and runs him to the other side of the Octagon. Great fight!